Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session A22: Turbulence Modeling: LES/RANS |
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Chair: Anne Staples, Virginia Polytechnic Institute and State University Room: 30C |
Sunday, November 18, 2012 8:00AM - 8:13AM |
A22.00001: A posteriori analysis of spatial filters for approximate deconvolution large eddy simulations of homogeneous incompressible flows Anne Staples, Omer San We investigate the effect of low-pass spatial filters for approximate deconvolution large eddy simulation (AD-LES) of turbulent incompressible flows. We propose the hyper-differential filter as a means of increasing the accuracy of the AD-LES model without increasing the computational cost. Box filters, Pade filters, and differential filters with a wide range of parameters are studied in the AD-LES framework. The AD-LES model, in conjunction with these spatial filters, is tested in the numerical simulation of the three-dimensional Taylor-Green vortex problem. The numerical results are benchmarked against direct numerical simulation (DNS) data. An under-resolved numerical simulation is also used for comparison purposes. According to the criteria used, the numerical results yield the following two conclusions: first, the AD-LES model equipped with any of these spatial filters yields accurate results at a fraction of the computational cost of DNS. Second, the most accurate results are obtained with the hyper-differential filter, followed by the differential filter. [Preview Abstract] |
Sunday, November 18, 2012 8:13AM - 8:26AM |
A22.00002: A ``true'' Unsteady RANS model of turbulence with inherent forcing Suad Jakirlic, Robert Maduta Usually, a turbulence model designed and calibrated in the steady RANS (Reynolds-Averaged Navier-Stokes) framework has been straightforwardly applied to an unsteady calculation. It ended up in a steady velocity field in the case of confined wall-bounded flows; a somewhat better outcome is to be expected in globally unstable flows, such as bluff body configurations. However, only a weakly unsteady mean flow can be returned with the level of unsteadiness being by far lower compared to a referent database. Presently, an instability-sensitive, eddy-resolving model based on a differential, near-wall Reynolds stress model of turbulence is formulated and applied to several attached and separated wall-bounded configurations -- channel and duct flows, external and internal flows separated from sharp-edged and continuous curved surfaces. In all cases considered the fluctuating velocity field was obtained started from the steady RANS results. The model proposed does not comprise any parameter depending explicitly on the grid spacing. An additional term in the corresponding length-scale determining equation providing a selective assessment of its production, modelled in terms of the von Karman length scale (comprising the second derivative of the velocity field) in line with the SAS (Scale-Adaptive Simulation) proposal (Menter and Egorov, 2010), represents here the key parameter. [Preview Abstract] |
Sunday, November 18, 2012 8:26AM - 8:39AM |
A22.00003: A-priori analysis of subgrid scalar flux models for turbulent high Schmidt number passive scalar mixing Siddhartha Verma, Guillaume Blanquart Numerical study of high Schmidt (Sc) number scalars using LES is hampered by the fact that few well-tested models exist specifically for this regime. Low Sc LES studies generally employ the widely used eddy-viscosity type models. However, these suffer from the fact that the resolved scalar gradient is often not well-aligned with the subgrid scalar flux (SGF). In this work, we perform an a-priori analysis based on Sc$\gg$1 simulations to explore the alignment of the SGF with the resolved as well as subgrid velocity and scalar quantities. Special attention is given to differences observed in the inertial-convective and the viscous-convective sub-ranges. These differences are related to the fundamental dissimilarities in the transport mechanisms. The alignment trends are used to ascertain the suitability of existing models for use in both sub-ranges. [Preview Abstract] |
Sunday, November 18, 2012 8:39AM - 8:52AM |
A22.00004: Implicit LES of turbulent flows with a high order discontinuous Galerkin method Simone Gremmo, Corentin Carton de Wiart, Bastien Gorissen, Koen Hillewaert, Gregoire Winckelmans, Gregory Coussement, Laurent Bricteux This study is concerned with the ability of a flow solver using a discontinuous Galerkin method (DGM) to perform large eddy simulation (LES) of turbulent flows. Several approaches are considered: the Smagorinsky model, a multiscale model, and implicit LES (ILES). First DGM is used to simulate 1D Burgers turbulence. This helps to analyze the spectral behavior of different subgrid scale (SGS) models. Energy spectra are obtained and compared to those obtained using a spectral code. It is shown that a moderate order (p=3,4) ILES-DGM approach provides sufficient dissipation concentrated only at the smallest resolved scales of the flow, preserving the larger scales. Second, results on homogeneous isotropic turbulence at very high Reynolds number also allow to highlight the scale selectivity of the approach. ILES-DGM provide energy spectra and energy decay results consistent with theory. At last the method is also validated on turbulent channel flow at $Re_{\tau}=395,\,590$. The results show a good agreement with the DNS of Moser et al. As a conclusion, for the present cases using a SGS model with DGM does not improve and can even degrade the results compared to ILES-DGM. Indeed, ILES-DGM already dissipates the small scales without influencing the larger turbulent structures. [Preview Abstract] |
Sunday, November 18, 2012 8:52AM - 9:05AM |
A22.00005: ABSTRACT WITHDRAWN |
Sunday, November 18, 2012 9:05AM - 9:18AM |
A22.00006: Model Invariance as a Basis for Hybrid LES-RANS Techniques Stephen Woodruff Advances in computing power have made hybrid Large-Eddy Simulation (LES) - Reynolds-Averaged Navier-Stokes (RANS) approaches feasible for practical problems where RANS methods alone are unsatisfactory. Hybrid methods have been most successful when RANS and LES regions can be placed so there is little interaction between them. A more effective computation would be one where LES regions are placed exactly where required by the physics. In the present work, model-invariant quantities are defined as combinations of the flow variables which yield physical results throughout the RANS/LES transition (such as the Reynolds stress, constructed from RANS and LES contributions). Model invariance provides a means for interpreting simulation results in RANS/LES transitions; the requirement that model invariance be preserved by the flow equations introduces terms that facilitate RANS/LES transitions and allow more freedom in placing those transitions. Numerical experiments are employed to demonstrate the ability of this approach to eliminate the mismatch seen between the RANS log law and the LES log law when hybrid techniques are applied to shear layers. The insensitivity of the approach to the choice of the RANS/LES blending function and other properties of the approach are also discussed [Preview Abstract] |
Sunday, November 18, 2012 9:18AM - 9:31AM |
A22.00007: Integral Methods for Validating RANS Models Daniel Israel Reynolds-averaged Navier-Stokes (RANS) models typically include multiple closure coefficients which are tuned by comparison to experimental data. For self-similar flows, this process can be simplified by examining similarity solutions of the RANS equations. A further simplification is to use approximate profiles inserted into the similarity equations. However, for problems without an asymptotic self-similar state, or for which we are interested in the initial transient response, these techniques cannot be used, leaving a tedious and computationally expensive parameter search through solutions of the original multi-dimensional flow problem. Classical integral methods provide a convenient alternative approach. Substituting a guessed approximate profile into the RANS equations directly, and integrating across the layer, yields ordinary differential equations for the integral properties of the profile. These simpler equations can be used to examine the behavior of the flow in various regimes and the effects of different parameter settings. [Preview Abstract] |
Sunday, November 18, 2012 9:31AM - 9:44AM |
A22.00008: Computational and Experimental Investigations of Flow past Spinning Cylinders Igbal Mehmedagic, Liam Buckley, Pasquale Carlucci, Donald Carlucci, Elias Aljalis, Siva Thangam An anisotropic two-equation Reynolds-stress model is developed by considering the modifications to the energy spectrum and through invariance based scaling. In this approach the effect of rotation is used to modify the energy spectrum, while the influence of swirl is modeled based on scaling laws. The resulting generalized model is validated for benchmark turbulent flows with swirl and curvature. The time-averaged equations of motion and energy are solved using the modeled form of transport equations for the turbulence kinetic energy and the scalar form of turbulence dissipation with an efficient finite-volume algorithm. Computations for flow past an axially rotating cylinder with a free-spinning base are performed along with experiments for a range of spin rates and free stream flow conditions. A subsonic wind tunnel with a forward-sting mounted spinning cylinder is used for experiments. The experimental results of Carlucci {\&} Thangam (2001) are used to benchmark flow over spinning cylinders. The data is extended to munitions spinning in the wake of other munitions and applications involving the design of projectiles are discussed. [Preview Abstract] |
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